Fast Content Delivery via Distributed Caching and Small Cell Cooperation

The demand for higher and higher wireless data rates is driven by the popularity of mobile video content delivery through wireless devices such as tablets and smartphones. To achieve unprecedented mobile content delivery speeds while reducing backhaul cost and delay, in this paper we propose a new system architecture that combines two recent ideas, distributed caching of content in small cells (FemtoCaching), and, cooperative transmissions from nearby base stations (Coordinated Multi-Point). A key characteristic of the proposed architecture is the interdependence between the caching strategy and the physical layer coordination. Specifically, the caching strategy may cache different content in nearby base stations (BSs) to maximize the cache hit ratio, or cache the same content in multiple nearby BSs such that the corresponding BSs can transmit concurrently, e.g., to multiple users using zero-forcing beamforming, and achieve multiplexing gains. Such interdependency allows a joint cross-layer optimization. Given the popularity distribution of the content, the available cache size, and the network topology, we devise near-optimal strategies of caching such that the system throughput is maximized or the system delay is minimized. Under realistic scenarios and assumptions, our analytical and simulation results show that our system yields significantly faster content delivery, which can be one order of magnitude faster than that of legacy systems.